Oracle interview Questions --- Part-2

14. What are the advantages of views?
- Provide an additional level of table security, by restricting access to a predetermined set of rows and columns of a table.
- Hide data complexity.
- Simplify commands for the user.
- Present the data in a different perspective from that of the base table.
- Store complex queries.

15. What is an Oracle sequence?
A sequence generates a serial list of unique numbers for numerical columns of a database's tables.

16. What is a synonym?
A synonym is an alias for a table, view, sequence or program unit.

17. What are the types of synonyms?
There are two types of synonyms private and public.

18. What is a private synonym?
Only its owner can access a private synonym.

19. What is a public synonym?
Any database user can access a public synonym.

20. What are synonyms used for?
- Mask the real name and owner of an object.
- Provide public access to an object
- Provide location transparency for tables, views or program units of a remote database.
- Simplify the SQL statements for database users.

21. What is an Oracle index?
An index is an optional structure associated with a table to have direct access to rows, which can be created to increase the performance of data retrieval. Index can be created on one or more columns of a table.

22. How are the index updates?
Indexes are automatically maintained and used by Oracle. Changes to table data are automatically incorporated into all relevant indexes.

23. What are clusters?
Clusters are groups of one or more tables physically stores together to share common columns and are often used together.

24. What is cluster key?
The related columns of the tables in a cluster are called the cluster key.

25. What is index cluster?
A cluster with an index on the cluster key.

26. What is hash cluster?
A row is stored in a hash cluster based on the result of applying a hash function to the row's cluster key value. All rows with the same hash key value are stores together on disk.